1. Field of the Invention
The present invention relates to an information storage device, and, in particular, to an information storage device in which the write current, which is used for writing data in a recording medium, changes in accordance with the temperature.
Recently, there has been progress in high-density recording and high-speed recording/reproducing in an information storage device such as a hard-disk drive. With the progress in high-density recording and high-speed recording/reproducing in an information storage device, it is requested to obtain an optimum write current, which is used for writing data in a recording medium. In a hard disk, magnetization characteristics change in accordance with a change in the temperature. For example, when the temperature rises, the coercive force Hc decreases, and thereby, it is possible to adequately magnetize the disk with a small write current. When the temperature falls, the coercive force Hc increases, and thereby, a large write current is needed to adequately magnetize the disk.
In a case where the coercive force Hc decreases, a recording medium is magnetized with a small write current. Therefore, when a large write current is supplied, surrounding portions are also magnetized to some degree. In a case where the coercive force Hc increases, a large write current is needed to magnetize a recording medium. Therefore, when a small write current is supplied, sufficient magnetization cannot be performed, and thus, information cannot be adequately recorded.
It is assumed that the optimum current is set for obtaining the highest recording density in a high temperature condition. In this case, in a low temperature condition, the set write current is not sufficient, and thereby, adequate information recording cannot be performed. It is assumed that the optimum write current is set for obtaining the highest recording density in a low temperature condition. In this case, in a high temperature condition, the set write current is so large that the write current influences surrounding recorded information. As a result, adequate information reading cannot be performed.
Accordingly, it is necessary to set the optimum write current in accordance with the temperature.
2. Description of the Related Art
FIG. 1 shows a block diagram of an example of a magnetic-disk device (hard-disk drive) in the related art.
The magnetic-disk device 10 is connected to a personal computer 30. Programs to be processed by the personal computer, processed data and so forth are magnetically recorded in magnetic disks 12 through magnetic heads 11. (Although, in the figure, only one magnetic disk 12 and one magnetic head 11 are indicated, actually, a plurality of magnetic disks 12 are stacked and two magnetic heads 11 are provided for each magnetic disk 12.) Such information magnetically recorded in the magnetic disks 12 is read and reproduced. The magnetic disks are fixed to a shaft of a spindle motor 13, and are rotated in the A direction by the spindle motor 13. Each of the magnetic heads 11 faces a respective one of the top surfaces and the bottom surfaces of the magnetic disks 12. Each magnetic head 11 magnetically affects a respective one of the top surface and the bottom surface of the magnetic disk 12 so as to record information in the magnetic disk 13. (The magnetic head 11 facing the bottom surface of the magnetic disk 12 is not shown in the figure.) Each magnetic head 11 also reads information recorded in the magnetic disk 12.
The magnetic heads 11 are supported by arms 14, respectively, and perform recording of information to and reproducing of information from the magnetic disks 12 in a condition where each magnetic head 11 slightly floats from the respective one of the top and bottom surfaces of the magnetic disks 12.
The ends of arms 14, opposite to the ends on which the magnetic heads 11 are fixed, form a part of a voice coil motor 15. By the voice coil motor 15, the arms 14 are rotated in radial directions (the arrow B directions) of the magnetic disks 12 about a rotation shaft 16. Thus, the arms 14 move the magnetic heads 11 in the radial directions on the magnetic disks 12. The magnetic heads 11 are connected with a head IC 18 via connection lines 17.
The head IC 18 amplifies recording signals to be supplied to the magnetic heads 11, and amplifies reproduced signals reproduced through the magnetic heads 11. The head IC 18 is connected with a read/write circuit 19. The read/write circuit 19 encodes data supplied by an MPU (Micro Processing Unit) 20 into recording signals, and decodes read signals read through the magnetic heads 11 into data which can be processed by the MPU 20.
The MPU 20 is connected with the read/write circuit 19, a DSP (Digital Signal Processor) 21 and a HDC (Hard disk Drive Controller) 22. The MPU 20 processes information to be recorded in the magnetic disks 12 and information reproduced from the magnetic disks 12. Further, the MPU 20 controls the rotation of the magnetic disks 12 and positioning of the magnetic heads 11 in accordance with information read from the magnetic disks 12.
The DSP 21 generates digital data for controlling the rotation of the spindle motor 13 in accordance with digital data which is supplied by the MPU 20 and determines the rotational speed of the magnetic disks 12. Further, the DSP 21 generates digital data for controlling the rotation angle of the voice coil motor 15 in accordance with digital data which is supplied by the MPU 20 and determines the positions of the magnetic heads 11.
The digital data for controlling the rotation of the spindle motor 13 and the digital data for controlling the rotation angle of the voice coil motor 15, generated by the DSP 21, is supplied to a DAC (Digital-to-Analog Converter) 23. The DAC 23 converts the digital data for controlling the rotation of the spindle motor 13 and the digital data for controlling the rotation angle of the voice coil motor 15, supplied by the DSP 21, into an analog signal.
The digital data for controlling the rotation of the spindle motor 13 supplied by the DSP 21 to the DAC 23 is converted into analog data by the DAC 23, as mentioned above, and then, this analog signal is supplied to a spindle-motor driving circuit 24. The spindle-motor driving circuit 24 generates a driving signal, for driving the spindle motor 13, in accordance with the analog signal supplied by the DAC 23, and supplies the driving signal to the spindle motor 13. The spindle motor 13 is driven and thus is rotated by the driving signal supplied from the spindle-motor driving circuit 24, and rotates the magnetic disks 12 in the arrow A direction at a fixed rotational speed.
The digital data for controlling the rotation angle of the voice coil motor 15 supplied by the DSP 21 to the DAC 23 is converted into analog data by the DAC 23, as mentioned above, and then, this analog signal is supplied to a voice-coil-motor driving circuit 25. The voice-coil-motor driving circuit 25 generates a driving signal, for driving the voice coil motor 15, in accordance with the analog signal supplied by the DAC 23, and supplies the driving signal to the voice coil motor 13. The driving signal supplied from the voice-coil-motor driving circuit 25 causes the voice coil motor 15 to control the rotation angle of the arms 14 in the arrow B directions and thus position the magnetic heads 11.
The HDC 22 is provided between the MPU 20 and a connector 26 which is used for external connection. The HDC 22 controls data transmission/reception between the magnetic-disk device 10 and external equipment connected to the connector 26. The connector 26 is connected with external equipment such as a personal computer 30 or the like. Via the connector 26, data and various control signals are input and output.
The magnetization characteristics of the magnetic disks 12 change due to a change of temperature. For example, when the temperature rises, the coercive force Hc decreases, and thereby, it is possible to adequately magnetize the magnetic disk with a small write current. When the temperature falls, the coercive force Hc increases, and thereby, a large write current is needed to adequately magnetize the magnetic disk.
In a case where the coercive force Hc decreases, a recording medium is magnetized with a small write current. Therefore, when a large write current is supplied, surrounding portions are also magnetized to some degree. In a case where the coercive force Hc increases, a large write current is needed to magnetize a recording medium. Therefore, when a small write current is supplied, sufficient magnetization cannot be performed, and thus, information cannot be adequately recorded.
According to a first scenario, is assumed that an optimum current is set for obtaining highest recording density in a high temperature condition. In this case, in a low temperature condition, the set write current is not sufficient, and thereby, adequate information recording cannot be performed. According to a second scenario, is assumed that the optimum write current is set for obtaining highest recording density in a low temperature condition. In this case, in a high temperature condition, the set write current is so large that the write current influences to surrounding recorded information. As a result, adequate information reading cannot be performed.
The above-described problems are pronounced in a hard-disk device, where a recording density is more than 5,000 TPI (Tracks Per Inch).
Accordingly, in the magnetic-disk device (hard-disk drive) 10 shown in FIG. 1, it has been difficult to increase the recording density.
In order to achieve a higher recording density and a larger recording capacity, for example, as disclosed in Japanese Laid-Open Patent Application Nos.60-143404, 1-317208, 5-258215, a method of changing the optimum write current in accordance with the temperature is disclosed.
However, in the recording devices disclosed in Japanese Laid-Open Patent Application Nos.60-143404, 1-317208, 5-258215, the ambient temperature of a magnetic head is detected and, when the ambient temperature of the magnetic head changes, the write current is set. Accordingly, the write current setting operation is performed so frequently that an ordinary information writing operation may not be performed adequately.